The selective 5-HT1B receptor inverse agonist 1'-methyl-5-[[2'-methyl-4'-(5-methyl-1,2, 4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl]-2,3,6,7-tetrahydro- spiro[furo[2,3-f]indole-3,4'-piperidine] (SB-224289) potently blocks terminal 5-HT autoreceptor function both in vitro and in vivo

Gadus morhua Eggs Sialoglycoprotein Prevent Estrogen Deficiency-Induced High Bone Turnover by Controlling OPG/RANKL/TRAF6 Pathway and Serum Metabolism

In recent years, the development of safe and effective anti-osteoporosis factors has attracted extensive attention. In this study, an estrogen-deficient osteoporosis rat model was employed to study the improving mechanism of sialoglycoprotein isolated from Gadus morhua eggs (Gds) against osteoporosis. The results showed that compared with OVX, Gds ameliorated the trabecular microstructure, especially the increased trabecular thickness, decreased trabecular separation, and enhanced the trabecular number. The analysis of qRT-PCR and western blotting found that Gds reduced bone resorption by inhibiting RANKL-induced osteoclastogenesis. The LC-MS/MS was used to investigate serum metabolism, and the enrichment metabolites were analyzed by the KEGG pathway. The results revealed that the Gds significantly altered the fat anabolism pathway, which includes ovarian steroidogenesis pathway and arachidonic acid metabolism pathway. Altogether, Gds could improve osteoporosis by suppressing high bone turnover via controlling OPG/RANKL/TRAF6 pathway, which is implicated with ovarian steroidogenesis pathway and arachidonic acid metabolism pathway. These findings indicated that Gds could be a candidate factor for anti-osteoporosis.

Subversion of Serotonin Receptor Signaling in Osteoblasts by Kynurenine Drives Acute Myeloid Leukemia

Remodeling of the microenvironment by tumor cells can activate pathways that favor cancer growth. Molecular delineation and targeting of such malignant-cell nonautonomous pathways may help overcome resistance to targeted therapies. Herein we leverage genetic mouse models, patient-derived xenografts, and patient samples to show that acute myeloid leukemia (AML) exploits peripheral serotonin signaling to remodel the endosteal niche to its advantage. AML progression requires the presence of serotonin receptor 1B (HTR1B) in osteoblasts and is driven by AML-secreted kynurenine, which acts as an oncometabolite and HTR1B ligand. AML cells utilize kynurenine to induce a proinflammatory state in osteoblasts that, through the acute-phase protein serum amyloid A (SAA), acts in a positive feedback loop on leukemia cells by increasing expression of IDO1-the rate-limiting enzyme for kynurenine synthesis-thereby enabling AML progression. This leukemia-osteoblast cross-talk, conferred by the kynurenine-HTR1B-SAA-IDO1 axis, could be exploited as a niche-focused therapeutic approach against AML, opening new avenues for cancer treatment.

SIGNIFICANCE

AML remains recalcitrant to treatments due to the emergence of resistant clones. We show a leukemia-cell nonautonomous progression mechanism that involves activation of a kynurenine-HTR1B-SAA-IDO1 axis between AML cells and osteoblasts. Targeting the niche by interrupting this axis can be pharmacologically harnessed to hamper AML progression and overcome therapy resistance. This article is highlighted in the In This Issue feature, p. 873.

Central 5-HT receptors and their function; present and future

Since our review of central 5-HT receptors and their function twenty years ago, no new 5-HT receptor has been discovered and there is little evidence that this situation will change in the near future. Nevertheless, over this time significant progress has been made in our understanding of the properties of these receptors and in the clinical translation of this information, and some of these developments are highlighted herein. Such highlights include extensive mapping of 5-HT receptors in both animal and human brain, culminating in readily-accessible brain atlases of 5-HT receptor distribution, as well as emerging data on how 5-HT receptors are distributed within complex neural circuits. Also, a range of important pharmacological and genetic tools have been developed that allow selective 5-HT receptor manipulation, in cells through to whole organism models. Moreover, unexpected complexity in 5-HT receptor function has been identified including agonist-dependent signalling that goes beyond the pharmacology of canonical 5-HT receptor signalling pathways set down in the 1980s and 1990s. This new knowledge of 5-HT signalling has been extended by the discovery of combined signalling of 5-HT and co-released neurotransmitters, especially glutamate. Another important advance has been the progression of a large number of 5-HT ligands through to experimental medicine studies and clinical trials, and some such agents have already become prescribed therapeutic drugs. Much more needs to be discovered and understood by 5-HT neuropharmacologists, not least how the diverse signalling effects of so many 5-HT receptor types interact with complex neural circuits to generate neurophysiological changes which ultimately lead to altered cognitions and behaviour. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

5-HT1B Receptor-Mediated Activation of ERK1/2 Requires Both Gαi/o and β-Arrestin Proteins

5-HT_1B receptors modulate synaptic serotonin (5-HT) levels and play a significant role in the regulation of emotional behaviors. These receptors are Gα_i/o-coupled and inhibit adenylyl cyclase but have also been reported to activate MAP kinases; however, the details of signaling cascades downstream of 5-HT_1B receptor activation remain unclear, particularly in neuronal cells. We generated a stable 5-HT_1B receptor-expressing Neuro2A (N2A-1B) neuronal cell line and demonstrate that activation of these receptors by the selective 5-HT_1B agonist CP-94253 results in activation of ERK1/2 but not of other closely related MAP kinases. Phosphoproteomics revealed four novel phosphorylation sites on the third intracellular loop of the 5-HT_1B receptor, and mutations of serine-256 and serine-291 to alanine led to reduced levels of ERK1/2 phosphorylation following receptor activation. Inhibition of Gα_i/o signaling with pertussis toxin, as well as MEK1/2 inhibition with U0126, also reduced 5-HT_1B-mediated ERK1/2 phosphorylation. Finally, we found that knockout of either β-arrestin 1 or β-arrestin 2 prevented 5-HT_1B-mediated phosphorylation of ERK1/2. Taken together, these results show that 5-HT_1B receptor activation selectively induces ERK1/2 activation through both the Gα_i subunit and β-arrestin proteins. This work elucidates the signal transduction pathway of 5-HT_1B receptors, as well as key phosphorylation sites within the receptor that modulate ERK1/2 activation, and further characterizes the intracellular mechanisms that underlie 5-HT_1B receptor function.

Recent Developments in the Synthesis, Chemistry and Applications of the Fully Unsaturated 1,2,4-Oxadiazoles

Recent major developments in the synthesis (including solid phase methodologies), chemistry and applications of the fully unsaturated 1,2,4-oxadiazole nucleus are reviewed. The review covers the years 1995–2000.

Pharmacological Modulations of the Serotonergic System in a Cell-Model of Familial Alzheimer's Disease

Serotonin (5-HT) plays a central role in the integrity of different brain functions. The 5-HT homeostasis is regulated by many factors, including serotonin transporter (SERT), monoamine oxidase enzyme (MAO), and several 5-HT receptors, including the 5-HT1B. There is little knowledge how the dynamics of this system is affected by the amyloid-β (Aβ) burden of Alzheimer's disease (AD) pathology. SH-SY5Y neuroblastoma cells transfected with the amyloid precursor protein (APP) gene containing the Swedish mutations causing familial AD (APPswe), were used as a model to explore the effect of Aβ pathology on 5-HT1B and related molecules including the receptor adaptor protein (p11), SERT and MAOA gene expression, and MAOA activity after treatment with selective serotonin reuptake inhibitor (SSRI) (sertraline), and a 5-HT1B receptor antagonist. Sertraline led more than 70 fold increase of 5-HT1B gene expression (p < 0.001), an increased serotonin turnover in both APPswe and control cells and reduced intracellular serotonin levels by 75% in APPswe cells but not in controls (p > 0.05). Treatment with the 5-HT1B receptor antagonist increased SERT gene-expression in control cells but not in the APPswe cells. 5-HT and 5-HT1B antagonist treatment resulted in different p11 expression patterns in APPswe cells compared to controls. Although MAOA gene expression was not changed by APPswe overexpression, adding 5-HT lead to a significant increase in MAOA gene expression in APPswe but not control cells. These findings suggest that the sensitivity of the 5-HT1B receptor and related systems is affected by APPswe overexpression, with potential relevance for pharmacologic intervention in AD. This may at least partly explain the lack of effect of SSRIs in patients with AD and depression.

Elaboration of tetra-orthogonally-substituted aromatic scaffolds towards novel EGFR-kinase inhibitors

Nitration of three regioisomers of bromo-fluorobenzaldehyde proceeds regioselectively, notably with H2SO4/HNO3 at 0 °C. The thereby synthesized tetrasubstituted aromatics, endowed with orthogonal substituents, can be elaborated via Pd-catalysed coupling, reduction and reductive amination reactions. As a test-case, these compounds were converted into EGFR inhibitors related to Gefitinib, whose activity was rationalised by docking studies.

5-HT2A receptors control body temperature in mice during LPS-induced inflammation via regulation of NO production

G protein-coupled 5-HT2A receptors are involved in the regulation of numerous normal and pathological physiological functions. At the same time, its involvement in the regulation of body temperature (Tb) in normal conditions is obscure. Here we study the effect of the 5-HT2A receptor activation or blockade on Tb in sick animals. The experiments were carried out on adult C57BL/6 mouse males. Systemic inflammation and sickness were produced by lipopolysaccharide (LPS, 0.1mg/kg, ip), while the 5-HT2A receptor was stimulated or blocked through the administration of the receptor agonist DOI or antagonist ketanserin (1mg/kg), respectively. LPS, DOI or ketanserin alone produced no effect on Tb. However, administration of LPS together with a peripheral or central ketanserin injection reduced Tb (32.2°C). Ketanserin reversed the LPS-induced expression of inducible NO synthase in the brain. Consequently, an involvement of NO in the mechanism of the hypothermic effect of ketanserin in sick mice was hypothesized. Administration of LPS together with NO synthase inhibitor, l-nitro-arginine methyl ester (60mg/kg, ip) resulted in deep (28.5°C) and prolonged (8h) hypothermia, while administration of l-nitro-arginine methyl ester alone produced no effect on Tb. Thus, 5-HT2A receptors play a key role in Tb control in sick mice. Blockade of this GPCR produces hypothermia in mice with systemic inflammation via attenuation of LPS-induced NO production. These results indicate an unexpected role of 5-HT2A receptors in inflammation and NO production and have a considerable biological impact on understanding the mechanism of animal adaptation to pathogens and parasites. Moreover, adverse side effects of 5-HT2A receptor antagonists in patients with inflammation may be expected.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Local potentiation of excitatory synapses by serotonin and its alteration in rodent models of depression

The causes of major depression remain unknown. Antidepressants elevate concentrations of monoamines, particularly serotonin, but it remains uncertain which downstream events are critical to their therapeutic effects. We found that endogenous serotonin selectively potentiated excitatory synapses formed by the temporoammonic pathway with CA1 pyramidal cells via activation of serotonin receptors (5-HT(1B)Rs), without affecting nearby Schaffer collateral synapses. This potentiation was expressed postsynaptically by AMPA-type glutamate receptors and required calmodulin-dependent protein kinase-mediated phosphorylation of GluA1 subunits. Because they share common expression mechanisms, long-term potentiation and serotonin-induced potentiation occluded each other. Long-term consolidation of spatial learning, a function of temporoammonic-CA1 synapses, was enhanced by 5-HT(1B)R antagonists. Serotonin-induced potentiation was quantitatively and qualitatively altered in a rat model of depression, restored by chronic antidepressants, and required for the ability of chronic antidepressants to reverse stress-induced anhedonia. Changes in serotonin-mediated potentiation, and its recovery by antidepressants, implicate excitatory synapses as a locus of plasticity in depression.

Integrated compound profiling screens identify the mitochondrial electron transport chain as the molecular target of the natural products manassantin, sesquicillin, and arctigenin

Phenotypic compound screens can be used to identify novel targets in signaling pathways and disease processes, but the usefulness of these screens depends on the ability to quickly determine the target and mechanism of action of the molecules identified as hits. One fast route to discovering the mechanism of action of a compound is to profile its properties and to match this profile with those of compounds of known mechanism of action. In this work, the Novartis collection of over 12,000 pure natural products was screened for effects on early zebrafish development. The largest phenotypic class of hits, which caused developmental arrest without necrosis, contained known electron transport chain inhibitors and many compounds of unknown mechanism of action. High-throughput transcriptional profiling revealed that these compounds are mechanistically related to one another. Metabolic and biochemical assays confirmed that all of the molecules that induced developmental arrest without necrosis inhibited the electron transport chain. These experiments demonstrate that the electron transport chain is the target of the natural products manassantin, sesquicillin, and arctigenin. The overlap between the zebrafish and transcriptional profiling screens was not perfect, indicating that multiple profiling screens are necessary to fully characterize molecules of unknown function. Together, zebrafish screening and transcriptional profiling represent sensitive and scalable approaches for identifying bioactive compounds and elucidating their mechanism of action.

NXN-188, a selective nNOS inhibitor and a 5-HT1B/1D receptor agonist, inhibits CGRP release in preclinical migraine models

BACKGROUND

NXN-188 is a combined neuronal nitric oxide synthase (nNOS) inhibitor and 5-hydroxytryptamine 1B/1D (5-HT1B/1D) receptor agonist. Using preclinical models, we evaluated whether these two unique therapeutic principles have a synergistic effect in attenuating stimulated calcitonin gene-related peptide (CGRP) release, a marker of trigeminal activation.

METHODS

We examined the effect of NXN-188 on: (1) KCl-, capsaicin- and resiniferatoxin (RTX)-induced immunoreactive CGRP (iCGRP) release from isolated preparation of rat dura mater, trigeminal ganglion (TG) and trigeminal nucleus caudalis (TNC); and (2) capsaicin- and electrical stimulation (ES)-induced middle meningeal artery (MMA) dilation in a rat closed-cranial window.

RESULTS

NXN-188 inhibited: (1) KCl-stimulated iCGRP release from dura mater (% decrease mean ± SEM, lowest effective concentration) (35 ± 6%, 30 µM), TG (24 ± 11%, 10 µM) and TNC (40 ± 8%, 10 µM); (2) capsaicin- and RTX-induced iCGRP release from dura mater; and (3) capsaicin- and ES-induced increase in dural artery diameter (32 ± 5%, 3 mg kg(-1) intravenous (i.v.) and 36 ± 1%, 10 mg kg(-1) i.v.).

CONCLUSIONS

NXN-188 inhibits CGRP release from migraine-relevant cephalic tissues. Its effect is most likely mediated via a combination of nNOS-inhibition and 5-HT1B/1D receptor agonism in dura mater while the mechanisms of action for inhibition of CGRP release from TG and TNC have to be investigated further.

Synthesis of novel 1,2,4-oxadiazoles and analogues as potential anticancer agents

A library of 3,5-disubstituted-1,2,4-oxadiazoles 7-9 and their bioisosters, 1,3,4-oxadiazole 14 and 1,3,4-thiadiazole 16, were synthesized and evaluated in vitro for their anticancer potential against a panel of six human cancer cell lines. The key step in the synthesis of oxadiazoles 7-9 involve coupling of amidoxime 6 with an appropriate carboxylic acid followed by thermal cyclization. The bioisosteres, 1,3,4-oxadiazole 14 and 1,3,4-thiadiazole 16 were prepared from the reaction of a common precursor diacylhydrazine 13 with thionyl chloride and Lawesson's reagent, respectively. The anticancer studies on the synthesized compounds revealed that presence of a cyclopentyloxy or n-butyloxy on the C-3 aryl ring and piperdin-4-yl or trichloromethyl at the C-5 position of 1,2,4-oxadiazole is essential for good activity. In particular, 1,2,4-oxadiazole 7i and analogue 1,3,4-thiadiazole 16 exhibited significant activity against DU145 (IC(50): 9.3 μM) and MDA-MB-231 (IC(50): 9.2 μM) cell lines, respectively.

5-HT(1B) receptor regulation of serotonin (5-HT) release by endogenous 5-HT in the substantia nigra

Axonal release of serotonin (5-hydroxytryptamine, 5-HT) in the CNS is typically regulated by presynaptic 5-HT autoreceptors. Release of 5-HT in substantia nigra pars reticulata (SNr), a principal output from the basal ganglia, has seemed an interesting exception to this rule. The SNr receives one of the highest densities of 5-HT innervation in mammalian brain and yet negative feedback regulation of axonal 5-HT release by endogenous 5-HT has not been identified here. We explored whether we could identify autoregulation of 5-HT release by 5-HT(1B) receptors in rat SNr slices using fast-scan cyclic voltammetry at carbon-fiber microelectrodes to detect 5-HT release evoked by discrete stimuli (50 Hz, 20 pulses) paired over short intervals (1-10 s) within which any autoreceptor control should occur. Evoked 5-HT release exhibited short-term depression after an initial stimulus that recovered by 10 s. Antagonists for 5-HT(1B) receptors, isamoltane (1 microM) or SB 224-289 (1 microM), did not modify release during a stimulus train, but rather, they modestly relieved depression of subsequent release evoked after a short delay (< or =2 s). Release was not modified by antagonists for GABA (picrotoxin, 100 microM, saclofen, 50 microM) or histamine-H(3) (thioperamide, 10 microM) receptors. These data indicate that 5-HT release can activate a 5-HT(1B)-receptor autoinhibition of subsequent release, which is mediated directly via 5-HT axons and not via GABAergic or histaminergic inputs. These data reveal that 5-HT release in SNr is not devoid of autoreceptor regulation by endogenous 5-HT, but rather is under modest control which only weakly limits 5-HT signaling.

Synthesis of novel quinolone and quinoline-2-carboxylic acid (4-morpholin-4-yl-phenyl)amides: A late-stage diversification approach to potent 5HT1B antagonists

Multiparallel amenable syntheses of 6-methoxy-8-amino-4-oxo-1,4-dihydroquinoline-2-carboxylic acid-(4-morpholin-4-yl-phenyl)amides (I) and 4-amino-6-methoxy-8-(4-methyl-piperazin-1-yl)-quinoline-2-carboxylic acid (4-morpholin-4-yl-phenyl)amides (II) which facilitate late-stage diversification at the 8-position of (I) and at the 4- and 8-positions of (II) are described. The resulting novel series were determined to contain potent 5HT(1B) antagonists. Preliminary SAR data are presented.

The structural evolution of dopamine D3 receptor ligands: structure-activity relationships and selected neuropharmacological aspects

"Evolution consists largely of molecular tinkering."-Following the famous concept of the molecular geneticist and medicine Nobel laureate François Jacob, in this review we describe the structural evolution of dopamine D3 receptor ligands from the natural agonist dopamine (DA) to highly potent and subtype selective new agents by bioisosteric tinkering with well-established and privileged or novel and fancy chemical functionalities and scaffolds. Some of the more than 200 ligands presented herein have already achieved therapeutic or scientific value up to now, some will most likely achieve it in the future. Hence, great importance is not only attached to the relationship between structure and activity of the ligands, but also to their utility as pharmacological tools in animal models or as therapeutics in patients with neurological diseases or other disorders.

5-HT-stimulated [35S]guanosine-5'-O-(3-thio)triphosphate binding as an assay for functional activation of G proteins coupled with 5-HT1B receptors in rat striatal membranes

Receptor-mediated guanine nucleotide-binding regulatory protein (G protein) activation or functional coupling between receptors and G proteins has been investigated by means of agonist-induced [35S]guanosine-5'-O-(3-thio)triphosphate ([35S]GTPgammaS) binding, especially for the receptor subtypes negatively coupled to adenylyl cyclase through Gi type G proteins. In the present study, 5-HT-stimulated [35S]GTPgammaS binding to rat stritatal membranes was pharmacologically characterized in detail with the help of an extensive series of 5-HT receptor ligands. The optimum experimental conditions for the concentrations of GDP, MgCl2 and NaCl in the assay buffer were initially determined, and the standard assay was performed with 20 microM GDP, 5 mM MgCl2 and 100 mM NaCl. The specific [35S]GTPgammaS binding was stimulated by several compounds that had been shown to be agonists at 5-HT(1B/1D) receptors. The negative logarithmic values of the concentration eliciting half-maximal effect (pEC50) for these agonists were significantly correlated with their pKi's reported in the previous study of 5-HT1B receptor binding in rat frontal cortical membranes. The increase in specific [35S]GTPgammaS binding in response to 1 microM 5-HT was potently inhibited by several 5-HT(1B/1D) receptor antagonists as well as beta-adrenoceptor antagonists such as S(-)-cyanopindolol. On the other hand, 3-[4-(4-chlorophenyl)piperazin-1-yl]-1,1-diphenyl-2-propanol HCl (BRL15572), a selective antagonist against human 5-HT1D receptors, was inactive as an antagonist at least up to 1 microM. Additionally, the concentration-response curve for 2-[5-[3-(4-methylsulphonylamino)benzyl-1,2,4-oxadiazol-5-yl]-1H-indol-3-yl]ethanamine (L694247) was shifted rightward in parallel by the addition of S(-)-cyanopindolol at concentrations of 10 and 100 nM, indicative of the competitive inhibitory manner. The specific [35S]GTPgammaS binding was reduced by 1'-methyl-5-([2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl)-2,3,6,7-tetrahydrospirospiro(furo[2,3-f]indole-3,4'-piperidine) (SB224289) and methiothepin in a concentration-dependent manner. The inhibitory curve by either compound was shifted to the right by 10 and 100 nM S(-)-cyanopindolol, suggesting that these two drugs behaved as inverse agonists at 5-HT1B receptors in the present functional assay system. 5-HT-stimulated [35S]GTPgammaS binding to rat striatal membranes serves as a simple but useful method of investigating the functional interaction between the native 5-HT1B receptors and their coupled G proteins in this brain region.

Synthesis of potent and selective serotonin 5-HT1B receptor ligands

A series of serotonin 5-HT1B ligands were synthesized and evaluated for their potency and selectivity against other 5-HT receptor subtypes. Many of these new compounds displayed high affinity and selectivity for the 5-HT1B receptor and compound 6c was found to have the in vitro binding profile necessary for development as a PET radioligand.

Synthesis and SAR of highly potent dual 5-HT1A and 5-HT1B antagonists as potential antidepressant drugs

Novel 5-HT(1) autoreceptor ligands based on the N-4-aryl-piperazinyl-N'-ethyl-5,6,7,8-tetrahydropyrido[4', 3':4,5]thieno[2,3-d]pyrimidin-4(3H)-one core are described. Aiming at antidepressants with a novel mode of action our objective was to identify potent antagonists showing balanced affinities and high selectivity for the 5-HT(1A) and 5-HT(1B) receptors. Strategies for the development of dual 5-HT(1A) and 5-HT(1B) antagonists based on 1 and 2 as leads and the corresponding results are discussed. Isoquinoline analogue 33 displayed high affinity and an antagonistic mode of action for the 5-HT(1A) and the 5-HT(1B) receptors and was characterized further with respect to selectivity, electrically stimulated [(3)H]5-HT release and in vivo efficacy.

Identification of a potent and selective 5-HT1B receptor antagonist

An SAR study around the mixed 5-HT1ABD receptor antagonist SB-272183 found that introduction of cis-2,6-dimethyl substitution onto the piperazine ring was a key structural change, which imparted a combination of both excellent selectivity over the 5-HT1A and 5-HT1D receptors and low intrinsic activity. This led to the identification of the selective 5-HT1B receptor antagonist SB-616234.

Postsynaptic 5-HT1B receptors modulate electroshock-induced generalised seizures in rats

1. Although an important regulatory role for serotonin (5-HT) in seizure activation and propagation is well established, relatively little is known of the function of specific 5-HT receptor subtypes on seizure modulation. 2. The aim of the present study was to investigate the role of 5-HT(1A, 1B and 1D) receptors in modulating generalised seizures in the rat maximal electroshock seizure threshold (MEST) test. 3. The mixed 5-HT receptor agonists SKF 99101 (5-20 mg kg(-1) i.p.) and RU 24969 (1-5 mg kg(-1) i.p.), 0.5 h pretest, both produced marked dose-related increases in seizure threshold. These agents share high affinity for 5-HT(1A, 1B and 1D) receptors. 4. Antiseizure effects induced by submaximal doses of these agonists were maintained following p-chlorophenylalanine (150 mg kg(-1) i.p. x 3 days)-induced 5-HT depletion. 5. The anticonvulsant action of both SKF 99101 (15 mg kg(-1) i.p.) and RU 24969 (2.5 mg kg(-1) i.p.) was dose-dependently abolished by the selective 5-HT1B receptor antagonist SB-224289 (0.1-3 mg kg(-1) p.o., 3 h pretest) but was unaffected by the selective 5-HT1A receptor antagonist WAY 100635 (0.01-0.3 mg kg(-1) s.c., 1 h pretest). This indicates that 5-HT1B receptors are primarily involved in mediating the anticonvulsant properties of these agents. 6. In addition, the ability of the 5-HT(1B/1D) receptor antagonist GR 127935 (0.3-3 mg kg(-1) s.c., 60 min pretest) to dose-dependently inhibit SKF 99101-induced elevation of seizure threshold also suggests possible downstream involvement of 5-HT1D receptors in the action of this agonist, although confirmation awaits the identification of a selective 5-HT1D receptor antagonist. 7. Overall, these data demonstrate that stimulation of postsynaptic 5-HT1B receptors inhibits electroshock-induced seizure spread in rats.

Structure-activity relationships of inverse agonists for G-protein-coupled receptors

It has been recently established that G-protein-coupled receptors (GPCRs) can be constitutively active, i.e., they can be active in the absence of an agonist. This activity can be inhibited by so-called inverse agonists. For a number of GPCRs, such inverse agonists have been developed and studied, now enabling for the first time a study into their structure-activity relationships.

Lack of association or linkage disequilibrium between schizophrenia and polymorphisms in the 5-HT1Dalpha and 5-HT1Dbeta autoreceptor genes: family-based association study

Genetic factors play a major role in the etiology of schizophrenia and disturbances of serotonergic pathways have been implicated in this disorder. The aim of the present study was to examine genetic association between schizophrenia and polymorphisms in the 5-HT1Dalpha (TaqI) and 5-HT1Dbeta (T261G and G861C) autoreceptor genes in ninety trios from Portugal. No association or linkage disequilibrium was obtained between schizophrenia and 5-HT1Dalpha and 5-HT1Dbeta autoreceptor genes with both haplotype relative risk (HRR) and transmission disequilibrium test (TDT). Concerning 5-HT1Dbeta autoreceptor gene, also negative results was obtained in the analysis of the haplotypes with transmit. Thus, our data provide no support for the hypothesis that polymorphisms at 5-HT1Dalpha (TaqI) and 5-HT1Dbeta (T261G and G861C) genes contributes to susceptibility to schizophrenia in the Portuguese population.

5-HT1B receptors, alpha2A/2C- and, to a lesser extent, alpha1-adrenoceptors mediate the external carotid vasoconstriction to ergotamine in vagosympathectomised dogs

It has previously been suggested that ergotamine produces external carotid vasoconstriction in vagosympathectomised dogs via 5-HT1B/1D receptors and alpha2-adrenoceptors. The present study has reanalysed this suggestion by using more selective antagonists alone and in combination. Fifty-two anaesthetised dogs were prepared for ultrasonic measurements of external carotid blood flow. The animals were divided into thirteen groups (n=4 each) receiving an i.v. bolus injection of, either physiological saline (0.3 ml/kg; control), or the antagonists SB224289 (300 microg/kg; 5-HT1B), BRL15572 (300 microg/kg; 5-HT1D), rauwolscine (300 microg/kg; alpha2), SB224289 + BRL15572 (300 microg/kg each), SB224289 + rauwolscine (300 microg/kg each), BRL15572 + rauwolscine (300 microg/kg each), rauwolscine (300 microg/kg) + prazosin (100 microg/kg; alpha1), SB224289 (300 microg/kg) + prazosin (100 microg/kg), SB224289 (300 microg/kg) + rauwolscine (300 microg/kg) + prazosin (100 microg/kg), SB224289 (300 microg/kg) + prazosin (100 microg/kg) + BRL44408 (1,000 microg/kg; alpha2A), SB224289 (300 microg/kg) + prazosin (100 microg/kg)+ imiloxan (1,000 microg/kg; alpha2B), or SB224289 (300 microg/kg) + prazosin (100 microg/kg) + MK912 (300 microg/kg; alpha2C). Each group received consecutive 1-min intracarotid infusions of ergotamine (0.56, 1, 1.8, 3.1, 5.6, 10 and 18 microg/min), following a cumulative schedule. In saline-pretreated animals, ergotamine induced dose-dependent decreases in external carotid blood flow without affecting arterial blood pressure or heart rate. These control responses were: unaffected by SB224289, BRL15572, rauwolscine or the combinations of SB224289 + BRL15572, BRL15572 + rauwolscine, rauwolscine + prazosin, SB224289 + prazosin, or SB224289 + prazosin + imiloxan; slightly blocked by SB224289 + rauwolscine; and markedly blocked by SB224289 + rauwolscine + prazosin, SB224289 + prazosin + BRL44408 or SB224289 + prazosin + MK912. Thus, the cranio-selective vasoconstriction elicited by ergotamine in dogs is predominantly mediated by 5-HT1B receptors as well as alpha2A/2C-adrenoceptor subtypes and, to a lesser extent, by alpha1-adrenoceptors.

Efficacy as a Vector: the Relative Prevalence and Paucity of Inverse Agonism

This article describes the expected phenotypic behavior of all types of ligands in constitutively active receptor systems and, in particular, the molecular mechanisms of inverse agonism. The possible physiological relevance of inverse agonism also is discussed. Competitive antagonists with the molecular property of negative efficacy demonstrate inverse agonism in constitutively active receptor systems. This is a phenotypic behavior that can only be observed in the appropriate assay; a lack of observed inverse agonism is evidence that the ligand does not possess negative efficacy only if it can be shown that constitutive receptor activity is present. In the absence of constitutive activity, inverse agonists behave as simple competitive antagonists. A survey of 105 articles on the activity of 380 antagonists on 73 biological G-protein-coupled receptor targets indicates that, in this sample dataset, 322 are inverse agonists and 58 (15%) are neutral antagonists. The predominance of inverse agonism agrees with theoretical predictions which indicate that neutral antagonists are the minority species in pharmacological space.

Ca2+ responses in Chinese hamster ovary-K1 cells demonstrate an atypical pattern of ligand-induced 5-HT1A receptor activation

Little experimental evidence has been reported for diverse signaling via 5-hydroxytryptamine (5-HT)1A receptors despite the fact that agonists seem to be more efficacious at dorsal raphe somatodendritic 5-HT1A autoreceptors than at postsynaptic 5-HT1A receptors. The present study investigated Ca2+ responses in Chinese hamster ovary (CHO)-K1 cells expressing a human 5-HT1A receptor by 5-HT, prototypical 5-HT1A agonists, N-(3-chloro-4-fluorobenzoyl)-4-fluoro-4-[(5-methyl-6-; methylaminopyridin-2-yl)-methylaminomethyl]-piperidine (F 14679), and especially N-(3-chloro-4-fluorobenzoyl)-4-fluoro-4-[(5-methylpyridin-2-yl)-; methylaminomethyl]piperidine (F 13640) as representative ligands of a new chemical class (methylamino-pyridine) that combines both high efficacy and selectivity for 5-HT1A receptors. 5-HT (pEC50 = 6.70 +/- 0.02) induced a pertussis toxin-sensitive, transient high-magnitude Ca2+ response. High-magnitude Ca2+ responses (Emax, percentage versus 5-HT) were also found with F 13640 (107 +/- 4), 5-carboxamidotryptamine (100 +/- 3), and F 14679 (87 +/- 3). In contrast, the prototypical 5-HT1A receptor agonists buspirone, ipsapirone, and 8-(hydroxy-2-(di-n-propylamino)tetralin, and also flesinoxan and eptapirone, were virtually inactive (< or =5). This atypical pattern of 5-HT1A receptor activation contrasts with the broad spectrum of the ligands' partial agonist properties as observed by measuring guanosine 5'-O-(3-[35 S]thio)triphosphate ([35S]GTPgammaS) binding responses with membranes of either CHO-K1 or C6-glial cells stably expressing a human 5-HT1A receptor. Remarkably, differences between ligands that seem small in the [35S]GTPgammaS binding assay translate into huge differences in the magnitude of Ca2+ responses. Therefore, some of these 5-HT1A ligands (i.e., F 13640) may in a selective way induce responses that may be not at all be achieved with other ligands (i.e., buspirone). In conclusion, the pharmacology of 5-HT1A receptor ligands seems to be codetermined by the effector pathway.

CCR2: characterization of the antagonist binding site from a combined receptor modeling/mutagenesis approach

We describe here a classical molecular modeling exercise that was carried out to provide a basis for the design of novel antagonist ligands of the CCR2 receptor. Using a theoretical model of the CCR2 receptor, docking studies were carried out to define plausible binding modes for the various known antagonist ligands, including our own series of indole piperidine compounds. On the basis of these results, a number of site-directed mutations (SDM) were designed that were intended to verify the proposed docking models. From these it was clear that further refinements would be necessary in the model. This was aided by the publication of a crystal structure of bovine rhodopsin, and a new receptor model was built by homology to this structure. This latest model enabled us to define ligand-docking hypotheses that were in complete agreement with the results of the SDM experiments.

Blockade of serotonin 5-HT1B and 5-HT2A receptors suppresses the induction of locomotor activity by 5-HT reuptake inhibitors, citalopram and fluvoxamine, in NMRI mice exposed to a novel environment: a comparison to other 5-HT receptor subtypes

RATIONALE

Though 5-HT plays an important role in the modulation of motor function, which is perturbed in depressive states, little is known concerning the influence of serotonin reuptake inhibitors (SSRIs) on locomotor activity (LA). Recently, we demonstrated that SSRIs, such as citalopram, enhance LA in mice exposed to a novel environment.

OBJECTIVES

This study examined the role of multiple classes of 5-HT receptor in citalopram-induced LA.

METHODS

The most selective antagonists currently available were used.

RESULTS

Citalopram-induced LA was dose-dependently attenuated by the 5-HT1B/1D receptor antagonists, S18127, GR125,743 and GR127,935, and by the selective 5-HT1B antagonist, SB224,289, but unaffected by the selective 5-HT1A antagonist, WAY100,635. The selective antagonists at 5-HT2A receptors, MDL100,907 and SR46,349 also dose-dependently attenuated induction of locomotion by citalopram, whereas the 5-HT2B antagonist, SB204,741, and the 5-HT2B/2C antagonist, SB206,553 were ineffective. Further, the selective 5-HT2C antagonist, SB242,084, potentiated the response to citalopram. Selective antagonists at 5-HT3 (ondansetron), 5-HT4 (GR125,487), 5-HT6 (SB271,046) and 5-HT7 (SB269,970) receptors did not significantly modify the action of citalopram. Underpinning these findings, SB224,289, GR125,743, MDL100,907 and SR46,349 likewise attenuated induction of locomotion by a further SSRI, fluvoxamine.

CONCLUSIONS

The locomotor response to SSRIs of mice exposed to a novel environment is mediated via 5-HT1B and 5-HT2A receptors. In view of the importance of motor function to the etiology and treatment of depression, the significance of these observations to the clinical actions of SSRIs will be of interest to elucidate.

h5-HT(1B) receptor-mediated constitutive Galphai3-protein activation in stably transfected Chinese hamster ovary cells: an antibody capture assay reveals protean efficacy of 5-HT

1. Serotonin 5-HT(1B) receptors couple to G-proteins of the Gi/o family. However, their activation of specific G-protein subtypes is poorly characterised. Using an innovative antibody capture/guanosine-5'-0-(3-[(35)S]thio)-triphosphate ([(35)S]GTPgammaS) binding strategy, we characterised Galpha(i3) subunit activation by h5-HT(1B) receptors stably expressed in Chinese hamster ovary (CHO) cells. 2. The agonists, 5-HT, alniditan and BMS181,101, stimulated Galpha(i3), whereas methiothepin and SB224,289 behaved as inverse agonists. The selective 5-HT(1B) receptor ligand, S18127, modestly stimulated Galpha(i3) and reversed the actions of both 5-HT and methiothepin. S18127 (1 micro M) also produced parallel, dextral shifts of the 5-HT and methiothepin isotherms. 3. Isotopic dilution experiments ([(35)S]GTPgammaS versus GTPgammaS) revealed high-affinity [(35)S]GTPgammaS binding to Galpha(i3) subunits in the absence of receptor ligands indicating constitutive activity. High-affinity [(35)S]GTPgammaS binding was increased 2.8-fold by 5-HT with an increase in the affinity of GTPgammaS for Galpha(i3) subunits. In contrast, methiothepin halved the number of high-affinity binding sites and decreased their affinity. 4. h5-HT(1B) receptor-mediated Galpha(i3) subunit activation was dependent on the concentration of NaCl. At 300 mM, 5-HT stimulated [(35)S]GTPgammaS binding, basal Galpha(i3) activation was low and methiothepin was inactive. In contrast, at 10 mM NaCl, basal activity was enhanced and the inverse agonist activity of methiothepin was accentuated. Under these conditions, 5-HT decreased Galpha(i3) activation. 5. In conclusion, at h5-HT(1B) receptors expressed in CHO cells: (i) inverse agonist induced inhibition of Galpha(i3), and its reversal by S18127, reveals constitutive activation of this Galpha subunit; (ii) constitutive Galpha(i3) activation can be quantified by isotopic dilution [(35)S]GTPgammaS binding and (iii) decreasing NaCl concentrations enhances Galpha(i3) activation and leads to protean agonist properties of 5-HT: that is a switch to inhibition of Galpha(i3).

An evaluation of the effect of NAS-181, a new selective 5-HT(1B) receptor antagonist, on extracellular 5-HT levels in rat frontal cortex

In the mammalian brain 5-HT(1B) receptors are present as autoreceptors regulating the release of serotonin (5-HT) by inhibitory feedback. The antagonistic properties of NAS-181 ((R)-(+)-2-[[[3-(Morpholinomethyl)-2H-chromen-8-yl]oxy]methyl] morpholine methane sulfonate), a new selective antagonist for the rodent 5-HT(1B) receptor, were determined by using an agonist-induced decrease of extracellular 5-HT. The 5-HT(1B) receptor agonist CP93129 (0.030.3 microM) applied by reversed microdialysis, dose-dependently reduced 5-HT levels in rat frontal cortex. The suppressant effect of CP93129 (0.1 microM) was smaller in the presence of fluvoxamine (3-10 microM), a 5-HT reuptake inhibitor. The effects of NAS-181 on CP93129 were compared with GR127935, a mixed 5-HT (1B/1D) receptor antagonist, and SB224289, a 5-HT(1B) receptor antagonist. Both in the presence and absence of fluvoxamine, the suppressant effect of CP93129 on extracellular 5-HT was attenuated by NAS-181 (1 microM) and GR127935 (10 microM), but not by SB224289 (1 microM). In the absence of fluvoxamine, GR127935, SB224289 and NAS-181 all reduced 5-HT levels, suggesting partial agonistic properties of these compounds. In conclusion, the results show that NAS-181 is a potent 5-HT(1B) receptor antagonist.

Origin and functional role of the extracellular serotonin in the midbrain raphe nuclei

There is considerable interest in the regulation of the extracellular compartment of the transmitter serotonin (5-hydroxytryptamine, 5-HT) in the midbrain raphe nuclei because it can control the activity of ascending serotonergic systems and the release of 5-HT in terminal areas of the forebrain. Several intrinsic and extrinsic factors of 5-HT neurons that regulate 5-HT release in the dorsal (DR) and median (MnR) raphe nucleus are reviewed in this article. Despite its high concentration in the extracellular space of the raphe nuclei, the origin of this pool of the transmitter remains to be determined. Regardless of its origin, is has been shown that the release of 5-HT in the rostral raphe nuclei is partly dependent on impulse flow and Ca(2+) ions. The release in the DR and MnR is critically dependent on the activation of 5-HT autoreceptors in these nuclei. Yet, it appears that 5-HT autoreceptors do not tonically inhibit 5-HT release in the raphe nuclei but rather play a role as sensors that respond to an excess of the endogenous transmitter. Both DR and MnR are equally responsive to the reduction of 5-HT release elicited by the local perfusion of 5-HT(1A) receptor agonists. In contrast, the effects of selective 5-HT(1B) receptor agonists are more pronounced in the MnR than in the DR. However, the cellular localization of 5-HT(1B) receptors in the raphe nuclei remains to be established. Furthermore, endogenous noradrenaline and GABA tonically regulate the extracellular concentration of 5-HT although the degree of tonicity appears to depend upon the sleep/wake cycle and the behavioral state of the animal. Glutamate exerts a phasic facilitatory control over the release of 5-HT in the raphe nuclei through ionotropic glutamate receptors. Overall, it appears that the extracellular concentration of 5-HT in the DR and the MnR is tightly controlled by intrinsic serotonergic mechanisms as well as afferent connections.

Specific labelling of serotonin 5-HT(1B) receptors in rat frontal cortex with the novel, phenylpiperazine derivative, [3H]GR125,743. A pharmacological characterization

Although several tritiated agonists have been used for radiolabelling serotonin (5-hydroxytryptamine, 5-HT)(1B) receptors in rats, data with a selective, radiolabelled antagonist have not been presented. Inasmuch as [3H]GR125,743 specifically labels cloned, human and native guinea pig 5-HT(1B) receptors and has been employed for characterization of cerebral 5-HT(1B) receptor in the latter species [Eur. J. Pharmacol. 327 (1997) 247.], the present study evaluated its utility for characterization of native, cerebral 5-HT(1B) sites in the rat. In homogenates of frontal cortex, [3H]GR125,743 (0.8 nM) showed rapid association (t(1/2)=3.4 min), >90% specific binding and high affinity (K(d)=0.6 nM) for a homogeneous population of receptors with a density (B(max)) of 160 fmol/mg protein. In competition binding studies, affinities were determined for 15 chemically diverse 5-HT(1B) agonists, including 2-[5-[3-(4-methylsulphonylamino)benzyl-1,2,4-oxadiazol-5-yl]-1H-indole-3-yl]ethylamine (L694,247; pK(i), 10.4), 5-carboxamidotryptamine (5-CT; 9.7), 3-[3-(2-dimethylamino-ethyl)-1H-indol-6-yl]-N-(4-methoxybenzyl)acrylamide (GR46,611; 9.6), 5-methoxy-3-(1,2,5,6-tetrahydro-4-pyridinyl)-1H-indole (RU24,969; 9.5), dihydroergotamine (DHE; 8.6), 5-H-pyrrolo[3,2-b]pyridin-5-one,1,4-dihydro-3-(1,2,3,6-tetrahydro-4-pyridinyl (CP93,129; 8.4), anpirtoline (7.9), sumatriptan (7.4), 1-[2-(3-fluorophenyl)ethyl]-4-[3-[5-(1,2,4-triazol-4-yl)-1H-indol-3-yl]propyl]piperazine (L775,606; 6.4) and (minus sign)-1(S)-[2-[4-(4-methoxyphenyl)piperazin-1-yl]ethyl]-N-methyl-3,4-dihydro-1H-2-benzopyran-6-carboxamide (PNU109,291; <5.0). Similarly, affinities were established for 13 chemically diverse antagonists, including N-[4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]-3-methyl-4-(4-pyridyl)benzamide (GR125,743; pK(i), 9.1), (-)cyanopindolol (9.0), (-)-tertatolol (8.2), N-(4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiozol-3-yl)biphenyl-4-carboxamide (GR127,935; 8.2), N-[3-(1,4-benzodioxan-5-yl)piperidin-4-yl]N-(indan-2yl)amine (S18127; 7.9), metergoline (7.8), (-)-pindolol (7.6), 1'-methyl-5-[2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-biphenyl-4-ylcarbonyl]-2,3,6,7-tetrahydro-5H-spiro[furo[2,3-f]indole-3,4'-piperidine] (SB224,289; 7.5) and ketanserin (<5.0). These rank orders of affinity correspond to the binding profile of 5-HT(1B) rather than 5-HT(1D) receptors. The low affinities of L775,066 and PNU109,291 versus L694,247 should be noted, as well as the low affinity of ketanserin as compared to SB224,289. Finally, in line with species differences, the affinities of several ligands including CP93,129, RU24,969, (-)-pindolol and (-)-propanolol in rat 5-HT(1B) sites were markedly different to guinea pig 5-HT(1B) sites labelled with [3H]GR125,743. In conclusion, [3H]GR125,743 is an appropriate tool for the radiolabelling of native, rat 5-HT(1B) receptors and permitted determination of the affinities of an extensive series of ligands at these sites.

Molecular, pharmacological and functional diversity of 5-HT receptors

Serotonin (5-hydroxytryptamine, 5-HT) is probably unique among the monoamines in that its effects are subserved by as many as 13 distinct heptahelical, G-protein-coupled receptors (GPCRs) and one (presumably a family of) ligand-gated ion channel(s). These receptors are divided into seven distinct classes (5-HT(1) to 5-HT(7)) largely on the basis of their structural and operational characteristics. Whilst this degree of physical diversity clearly underscores the physiological importance of serotonin, evidence for an even greater degree of operational diversity continues to emerge. The challenge for modern 5-HT research has therefore been to define more precisely the properties of the systems that make this incredible diversity possible. Much progress in this regard has been made during the last decade with the realisation that serotonin is possibly the least conservative monoamine transmitter and the cloning of its many receptors. Coupled with the actions of an extremely avid and efficient reuptake system, this array of receptor subtypes provides almost limitless signalling capabilities to the extent that one might even question the need for other transmitter systems. However, the complexity of the system appears endless, since posttranslational modifications, such as alternate splicing and RNA editing, increase the number of proteins, oligomerisation and heteromerisation increase the number of complexes, and multiple G-protein suggest receptor trafficking, allowing phenotypic switching and crosstalk within and possibly between receptor families. Whether all these possibilities are used in vivo under physiological or pathological conditions remains to be firmly established, but in essence, such variety will keep the 5-HT community busy for quite some time. Those who may have predicted that molecular biology would largely simplify the life of pharmacologists have missed the point for 5-HT research in particular and, most probably, for many other transmitters. This chapter is an attempt to summarise very briefly 5-HT receptor diversity. The reward for unravelling this complex array of serotonin receptor--effector systems may be substantial, the ultimate prize being the development of important new drugs in a range of disease areas.

The role of 5-HT1B receptors in the regulation of serotonin cell firing and release in the rat brain

The release of 5-HT in terminal areas of the rodent brain is regulated by 5-HT1B receptors. Here we examined the role of 5-HT1B receptors in the control of 5-HT output and firing in the dorsal raphe nucleus (DR), median raphe nucleus (MnR) and forebrain of the rat in vivo. The local perfusion (30-300 microM) of the selective 5-HT1B receptor agonist CP-93,129 to freely moving rats decreased 5-HT release in the DR and more markedly in the MnR. Likewise, 300 microM CP-93,129 reduced 5-HT output in substantia nigra pars reticulata, ventral pallidum, lateral habenula and the suprachiasmatic nucleus. The effect of CP-93,129 was prevented by SB-224289, but not by WAY-100635, selective 5-HT1B and 5-HT1A receptor antagonists, respectively. SB-224289 did not alter dialysate 5-HT in any raphe nuclei. The intravenous administration of the brain-penetrant selective 5-HT1B receptor agonist CP-94,253 (0.5-2.0 mg/kg) to anesthetized rats decreased dialysate 5-HT in dorsal hippocampus and globus pallidus, increased it in MnR and left it unaltered in the DR and medial prefrontal cortex. SB-224289, at a dose known to block 5-HT1B autoreceptor-mediated effects (5 mg/kg), did not prevent the effect of CP-94,253 on MnR 5-HT. The intravenous administration of CP-94,253 (0.05-1.6 mg/kg) to anesthetized rats increased the firing rate of MnR, but not DR-5-HT neurons. The local perfusion of CP-94,253 in the MnR showed a biphasic effect, with 5-HT reductions at 0.3-3 microM and increase at 300 microM. These results suggest that 5-HT cell firing and release in midbrain raphe nuclei (particularly in the MnR) are under control of 5-HT1B receptors. The activation of 5-HT1B autoreceptors (possibly located on 5-HT nerve endings and/or varicosities within DR and MnR) reduces 5-HT release. The effects of higher concentrations of 5-HT1B receptor agonists seem more compatible with the activation of 5-HT1B heteroreceptors on inhibitory neurons.

Molecular cloning, pharmacological properties and tissue distribution of the porcine 5-HT(1B) receptor

Using a combination of RT - PCR and inverse-PCR techniques, we amplified, cloned and sequenced a full-length porcine 5-HT(1B) receptor cDNA derived from porcine cerebral cortex. Sequence analysis revealed 1170 bp encoding an open reading frame of 390 amino acids showing a 95% similarity with the human 5-HT(1B) receptor. The recombinant porcine 5-HT(1B) cDNA was expressed in monkey Cos-7 cells and its pharmacological profile was determined by radioligand binding assay using [(3)H]-GR125743. The affinities of several agonists (L694247>ergotamine > or =5-carboxamidotryptamine=dihydroergotamine=5-HT>CP122638=zolmitriptan>sumatriptan) and putative antagonists (GR127935>methiothepin>SB224289>>ritanserin>ketanserin > or =BRL15572) correlated highly with those described for the recombinant human 5-HT(1B) receptor. In membranes obtained from cells co-expressing the porcine 5-HT(1B) receptor and a mutant G(alphao)Cys(351)Ile protein, 5-HT and zolmitriptan increased, while the 5-HT(1B) receptor antagonist SB224289 decreased basal [(35)S]-GTPgammaS binding, thus showing inverse agonism. The potency of zolmitriptan in the [(35)S]-GTPgammaS binding assay (pEC(50): 7.64+/-0.04) agreed with its affinity in displacing the antagonist [(3)H]-GR125743 (pK(i): 7.36+/-0.07). The 5-HT(1B) receptor mRNA was observed by RT-PCR in several blood vessels, cerebral cortex, cerebellum and trigeminal ganglion. In situ hybridization performed in frontal cerebral cortex sections revealed the expression of 5-HT(1B) receptor mRNA in pyramidal cells. In conclusion, we have cloned and established the amino acid sequence, ligand binding profile and location of the porcine 5-HT(1B) receptor. This information may be useful in exploring the role of 5-HT(1B) receptor in pathophysiological processes relevant for novel drug discovery in diseases such as migraine.

Stepwise Modulation of Neurokinin-3 and Neurokinin-2 Receptor Affinity and Selectivity in Quinoline Tachykinin Receptor Antagonists

A stepwise chemical modification from human neurokinin-3 receptor (hNK-3R)-selective antagonists to potent and combined hNK-3R and hNK-2R antagonists using the same 2-phenylquinoline template is described. Docking studies with 3-D models of the hNK-3 and hNK-2 receptors were used to drive the chemical design and speed up the identification of potent and combined antagonsits at both receptors. (S)-(+)-N-(1-Cyclohexylethyl)-3-[(4-morpholin-4-yl)piperidin-1-yl]methyl-2-phenylquinoline-4-carboxamide (compound 25, SB-400238: hNK-3R binding affinity, K(i) = 0.8 nM; hNK-2R binding affinity, K(i) = 0.8 nM) emerged as the best example in this approach. Further studies led to the identification of (S)-(+)-N-(1,2,2-trimethylpropyl)-3-[(4-piperidin-1-yl)piperidin-1-yl]methyl-2-phenylquinoline-4-carboxamide (compound 28, SB-414240: hNK-3R binding affinity, K(i) = 193 nM; hNK-2R binding affinity, K(i) = 1.0 nM) as the first hNK-2R-selective antagonist belonging to the 2-phenylquinoline chemical class. Since some members of this chemical series showed a significant binding affinity for the human mu-opioid receptor (hMOR), docking studies were also conducted on a 3-D model of the hMOR, resulting in the identification of a viable chemical strategy to avoid any significant micro-opioid component. Compounds 25 and 28 are therefore suitable pharmacological tools in the tachykinin area to elucidate further the pathophysiological role of NK-3 and NK-2 receptors and the therapeutic potential of selective NK-2 (28) or combined NK-3 and NK-2 (25) receptor antagonists.

Could the 5-HT1B receptor inverse agonism affect learning consolidation?

Diverse evidence indicates that, the 5-HT system might play a role in learning and memory, since it occurs in brain areas mediating such processes and 5-HT drugs modulate them. Hence in this work, in order to explore further 5-HT involvement on learning and memory 5-HT1B receptors' role is investigated. Evidence indicates that SB-224289 (a 5-HT1B receptor inverse agonist) post-training injection facilitated learning consolidation in an associative autoshaping learning task, this effect was partially reversed by GR 127935 (a 5-HT1B/1D receptor antagonist), but unaffected by MDL 100907 (a 5-HT2A receptor antagonist) or ketanserin (a 5-HT1D/2A/7 receptor antagonist) at low doses. Moreover, SB-224289 antagonized the learning deficit produced by TFMPP (a 5-HT1A/1B/1D/2A/2C receptor agonist), GR 46611 (a 5-HT1A/1B/1D receptor agonist), mCPP (a 5-HT2A/2C/3/7 receptor agonist/antagonist) or GR 127935 (at low dose). SB-224289 did not alter the 8-OH-DPAT (a 5-HT1A/7 receptor agonist) learning facilitatory effect. SB-224289 eliminated the deficit learning produced by the anticholinergic muscarinic scopolamine or the glutamatergic antagonist dizocilpine. Administration of both, GR 127935 (5mg/kg) plus ketanserin (0.01 mg/kg) did not modify learning consolidation; nevertheless, when ketanserin dose was increased (0.1-1.0mg/kg) and SB-224289 dose was maintained constant, a learning facilitation effect was observed. Notably, SB-224289 at 1.0mg/kg potentiated a subeffective dose of the 5-HT1B/1D receptor agonist/antagonist mixed GR 127935, which facilitated learning consolidation and this effect was abolished by ketanserin at a higher dose. Collectively, the data confirm and extend the earlier findings with GR 127935 and the effects of non-selective 5-HT(1B) receptor agonists. Clearly 5-HT1B agonists induced a learning deficit which can be reversed with SB-224289. Perhaps more importantly, SB-224289 enhances learning consolidation when given alone and can reverse the deficits induced by both cholinergic and glutamatergic antagonist. Hence, 5-HT1B receptor inverse agonists or antagonists could represent drugs for the treatment of learning and memory dysfunctions.

Constitutive activity at serotonin 5-HT(1D) receptors: detection by homologous GTPgammaS versus [(35)S]-GTPgammaS binding isotherms

Although many G-protein-coupled receptors (GPCRs) may display constitutive activity, their detection has, to date, depended on the use of inverse agonists. The present study exploited a novel procedure to investigate constitutive activity at recombinant human (h) serotonin (5-HT) 5-HT(1D) receptors stably expressed in Chinese hamster ovary (CHO) cells. 5-HT modestly stimulated guanosine-5'-O-(3-[(35)S]thio)-triphosphate ([(35)S]-GTPgammaS) binding to CHO-h5-HT(1D) membranes whereas methiothepin and the 5-HT(1B/1D)-selective ligand, SB224,289, exerted robust inhibition of basal [(35)S]-GTPgammaS binding (inverse agonism). These actions were specific inasmuch as they were reversed by the novel, selective 5-HT(1B/1D) ligand, S18127. Constitutive activity was investigated by homologous inhibition of [(35)S]-GTPgammaS binding to CHO-h5-HT(1D) membranes with unlabelled GTPgammaS. Under 'basal' conditions (absence of receptor ligand), biphasic isotherms were observed. Most (80%) [(35)S]-GTPgammaS binding sites were in the high affinity (HA) versus low affinity (LA) component of the isotherms. HA binding was augmented by 5-HT (to 155%; relative to basal values=100%), but decreased by methiothepin (to 23%) and by SB224,289 (to 67%). In contrast, LA binding was not altered. Further, membranes of untransfected CHO cells exhibited only LA binding sites, indicating that the latter are not related to h5-HT(1D) receptor-G-protein coupling. Thus, at 5-HT(1D) receptors expressed in this CHO cell line, HA binding detected in homologous inhibition experiments (GTPgammaS versus [(35)S]-GTPgammaS) under basal conditions provides a measure of constitutive G-protein activation. Thus, it is suggested that for h5-HT(1D) receptors and, possibly, other GPCRs, inverse agonists will be detectable by [(35)S]-GTPgammaS binding if a HA component is present under basal conditions.

Regulation of sensitivity to 5-hydroxytryptamine in pulmonary supernumerary but not conventional arteries by a 5-HT(1D)-like receptor

Bovine pulmonary supernumerary arteries are more sensitive to 5-hydroxtryptamine (5-HT) (pD(2) 6.43+/-0.25) than conventional arteries (pD(2) 5.32+/-0.16). This study investigated receptors for 5-HT in ring segments of these arteries. The 5-HT(2) receptor agonist, 2,5 dimethoxy-4-iodoamphetamine hydrobromide (DOI) constricts both arteries. The selective 5-HT(2) receptor antagonist ritanserin produced insurmountable antagonism of 5-HT concentration-response curves in both arteries, whereas the 5-HT(1B/1D) receptor antagonist N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'(5-methyl- 1,2,4-oxadiazol-3-yl[1,1,-biphenyl]-4-carboxamide hydrochloride (GR127935) produced much greater antagonism in supernumerary arteries. In rings preconstricted with 9,11-dideoxy-9, 11-methanoepoxy prostalagdin F(2alpha) (U46619) and relaxed with the adenylyl cyclase activator forskolin, the selective 5-HT(ID) receptor agonist 2-[5-[3-(4-methylsulphonylamino) benzyl-1,2, 4-oxadiazol-5-yl]-1H-indole-3-yl] ethylamine (L694247) reversed the relaxation. Concentration-response curves for L694247-induced reversal of forskolin-relaxation were antagonised by GR127935 in supernumerary (pK(B) 8.6) and conventional (pK(B) 8.4) arteries, whereas concentration-response curves to 5-HT-were less sensitive to antagonism by GR127935T and this was more obvious in conventional (pK(B) 7.6) than supernumerary (pK(B) 8.1) arteries. Neither the selective 5-HT(1D) receptor antagonist (1-(3-chlorophenyl)-4-[3, 3-diphenyl (2-(S,R) hydroxypropanyl)piperazine] hydrochloride (BRL15572) nor the 5-HT(1B) receptor antagonist (2,3,6, 7-tetrahydro-1'-methyl-5-[2'methyl-4'5-(methyl-1,2,4-oxadiazol-3-y l) biphenyl-4-carbonyl]furo[2,3-f]indole-3-spiro-4'-piperidine hydrochloride (SB224289) antagonised concentration-response curves induced by 5-HT or 5-HT(1)-receptor-selective agonists. In addition to the 5-HT(2A) receptor, 5-HT activates a GR127935-sensitive and a GR127935-insensitive receptor in these arteries. Supernumerary arteries have a greater proportion of GR127935-sensitive receptors, which display only some of the pharmacological characteristics of the cloned 5-HT(ID) receptor. It is possible that the GR127935-sensitive receptor could be a species homologue of the human 5-HT(1B) receptor that is insensitive to SB224289.

Molecular cloning, sequence analysis and pharmacological properties of the porcine 5-HT(1D) receptor

A cDNA encoding the full-length 5-HT(1D) receptor derived from porcine cerebral cortex was amplified, cloned and sequenced, using guinea-pig 5-HT(1D) receptor coding sequence oligonucleotide primers in reverse transcription-polymerase chain reaction (RT - PCR). The 5' and 3' ends of the porcine 5-HT(1D) receptor cDNA were verified by inverse PCR. Sequence analysis of porcine 5-HT(1D) receptor cDNA revealed an open reading frame of 1134 nucleotides encoding a polypeptide of 377 amino acids having 92% homology with the human 5-HT(1D) receptor and 88 - 90% homology with other species homologues. The porcine 5-HT(1D) receptor cDNA was further subcloned into a mammalian expression vector pcDNA3 and expressed in monkey Cos-7 cells. Radioligand binding assays using either [(3)H]-5-CT or [(3)H]-GR125743 on Cos-7 cell membranes showed that pK(i) values of 14 serotonin ligands were highly correlated with those obtained with the human 5-HT(1D) receptor. Nonetheless, a selective antagonist at the human 5-HT(1D) receptor, BRL15572, only poorly recognized the porcine homologue. Using membranes from cells co-expressing the porcine 5-HT(1D) receptor and rat G(alphail)Cys(351) Ile protein, it was shown that 5-HT and zolmitriptan increased, while ketanserin decreased basal [(35)S]-GTPgammaS binding. The potency of zolmitriptan in the [(35)S]-GTPgammaS binding assay (pEC(50): 8. 46+/-0.08) agreed with its affinity in displacing the radioligands [(3)H]-5-CT and [(3)H]-GR125743 (pK(i): 8.38+/-0.15 and 8.67+/-0.08, respectively). In conclusion, we have established the cDNA sequence and pharmacology of the cloned porcine 5-HT(1D) receptor. This information would be useful in exploring the role of divergent amino acid residues in the receptor-ligand interaction as well as the role of 5-HT(1D) receptor in pathophysiological processes relevant for novel drug discovery in diseases such as migraine.

Inverse agonism and constitutive activity as functional correlates of serotonin h5-HT(1B) receptor/G-protein stoichiometry

This study evaluated the influence of receptor/G-protein (R:G) stoichiometry on constitutive activity and the efficacy of agonists, partial agonists, and inverse agonists at human (h) 5-hydroxytryphamine 1B (5-HT(1B)) receptors. Two Chinese hamster ovary cell lines were used; they expressed 8.5 versus 0.4 pmol h5-HT(1B) receptors/mg (determined by [(3)H]GR125,743 saturation analysis) and 3.0 versus 1.5 pmol receptor-activated G-proteins/mg [determined by guanosine-5'-O-(3-[(35)S]thio)-triphosphate ([(35)S]GTPgammaS) isotopic dilution], respectively. Thus, they displayed R:G ratios of approximately 3.0 (RGhigh) and approximately 0.3 (RGlow), respectively. In competition-binding experiments, the agonists, 5-HT and sumatriptan, displayed fewer high-affinity (HA)-binding sites and the partial agonists, BMS181, 101 and L775,606, displayed decreased affinity in RGhigh versus RGlow membranes. In contrast, the inverse agonists, SB224,289 and, to a lesser extent, methiothepin, showed increased affinity. In G-protein activation experiments, both basal and 5-HT-activated [(35)S]GTPgammaS binding were higher in RGhigh than in RGlow membranes. Constitutive activity (determined by inhibition of basal [(35)S]GTPgammaS binding with GTPgammaS in the absence of receptor ligands) was more pronounced in RGhigh versus RGlow membranes, as revealed by the >5-fold greater proportion of HA sites. Correspondingly, the negative efficacy of inverse agonists was strikingly augmented, inasmuch as they suppressed approximately two-thirds of HA [(35)S]GTPgammaS binding in RGhigh membranes, but only approximately one-third in RGlow membranes. Furthermore, the efficacy of partial agonists was greater at RGhigh versus RGlow membranes, as estimated by their ability to enhance [(35)S]GTPgammaS binding. In conclusion, an increase in R:G ratios at h5-HT(1B) receptors was associated with an increase in relative efficacy of partial agonists and, most notably, an increase in both constitutive G-protein activation and negative efficacy of inverse agonists.

The possible role of 5-HT(1B/D) receptors in psychiatric disorders and their potential as a target for therapy

Serotonin (5-hydroxytryptamine, 5-HT) is implicated in several psychiatric diseases. Is this also true for 5-HT(1B/D) receptors? These receptors are found in high density in substantia nigra, globus pallidus, striatum and basal ganglia and in other brain regions. This ubiquity makes 5-HT(1B/D) receptors responsible for many physiological and behavioural functions. This review focuses on the role of 5-HT(1B) receptors in the regulation of 5-HT release and synthesis. Microdialysis experiments performed on freely moving animals are an interesting in vivo model to study the function of the terminal 5-HT(1B) autoreceptor. Synthesis of 5-HT, estimated by the measurement of the accumulation of 5-hydroxytryptophan (5-HTP) ex vivo or in vitro, is modulated by the 5-HT(1B) autoreceptors. Many reports have shown that chronic administration with selective serotonin reuptake inhibitors leads to the desensitisation of the terminal 5-HT(1B) autoreceptors. With the help of some animal models of depression and anxiety and with some data from clinical studies it has been hypothesised that 5-HT(1B) receptors may be supersensitive in depression, anxiety and obsessive compulsive disorder. Thus, since the dysfunction of 5-HT(1B) receptors may be involved in some pathological states, particularly in the psychiatric field, these receptors represent important potential targets for drugs to treat mental diseases.

Characterization of SB-271046: a potent, selective and orally active 5-HT(6) receptor antagonist

SB-271046, potently displaced [(3)H]-LSD and [(125)I]-SB-258585 from human 5-HT(6) receptors recombinantly expressed in HeLa cells in vitro (pK(i) 8.92 and 9.09 respectively). SB-271046 also displaced [(125)I]-SB-258585 from human caudate putamen and rat and pig striatum membranes (pK(i) 8.81, 9.02 and 8.55 respectively). SB-271046 was over 200 fold selective for the 5-HT(6) receptor vs. 55 other receptors, binding sites and ion channels. In functional studies on human 5-HT(6) receptors SB-271046 competitively antagonized 5-HT-induced stimulation of adenylyl cyclase activity with a pA(2) of 8.71. SB-271046 produced an increase in seizure threshold over a wide-dose range in the rat maximal electroshock seizure threshold (MEST) test, with a minimum effective dose of < or =0.1 mg kg(-1) p.o. and maximum effect at 4 h post-dose. The level of anticonvulsant activity achieved correlated well with the blood concentrations of SB-271046 (EC(50) of 0.16 microM) and brain concentrations of 0.01-0.04 microM at C(max). These data, together with the observed anticonvulsant activity of other selective 5-HT(6) receptor antagonists, SB-258510 (10 mg kg(-1), 2-6 h pre-test) and Ro 04-6790 (1-30 mg kg(-1), 1 h pre-test), in the rat MEST test, suggest that the anticonvulsant properties of SB-271046 are likely to be mediated by 5-HT(6) receptors. Overall, these studies demonstrate that SB-271046 is a potent and selective 5-HT(6) receptor antagonist and is orally active in the rat MEST test. SB-271046 represents a valuable tool for evaluating the in vivo central function of 5-HT(6) receptors.